Process for increasing the scuffresistance of paperboard



3,457,100 PROCESS FOR INCREASING THE SCUFF- RESISTANCE OF PAPERBOARD Leon Levene, Toledo, Ohio, assignor to Owens-Illinois, Inc., a corporation of Ohio No Drawing. Filed Aug. 16, 1965, Ser. No. 480,196 Int. Cl. D21h U34, U48 US. Cl. 117-76 1 Claim ABSTRACT OF THE DISCLOSURE This invention relates to a process for imparting scuffresistant properties to paperboard and the paperboard resulting from the process. The process generally comprises the treating of a paperboard substrate with an effective amount of solution of a tin compound, for example, a solution of stannous chloride. The paperboard is then dried and treated with an aqueous emulsion of polyethylene. Upon drying, a scuff-resistant paperboard product results.

This invention relates to paper and paperboard. In particular, the invention pertains to a method and composition for increasing the scuff resistance of paper and paperboard.

Paper and paperboard type products are commercially used for the manufacture of containers such as bags, setup boxes, folding cartons, fiber cans and tubes, corrugated and solid fiber boxes, wardrobes and drums. Paper and paperboard occasionally shows a pronounced and distinct tendency to form quills or peels when subjected to scufiing or rubbing in passing through the corrugator, on the conveyor system, and in the freight cars where one box rubs against another. Also, during shipe ment the article of manufacture within the container often comes into contact with the abrasive nature of the paperboard, and the surface of the article of manufacture being shipped is often detrimentally affected, that is, the coarse surface of the container causes wear spots, scufi's, scratches and other undesirable types of marks and flaws on the article.

These problems are very serious as the paperboard might fail or perform unsatisfactorily under the desired conditions. Also, the shipped article has to be repaired or resurfaced prior to sale. The latter problems are par-. ticularly acute with items such as clothes, bowling balls, furniture, appliances, etc.

Attempts have been made to make-paper scuff-resistant. Drying-oil coatings, cooked varnishes, and solutions of natural gums in suitable solvents have been applied to paper for adding scuff resistance. These coatings were generally hard, brittle, adversely affected by temperature and humidity, inclined to be tacky and malodorous. Other ill-fated attempts have been made to apply certain com-v pounds to paper and paperboard so as to impart a nonabrasive surface to said paper or paperboard. These coating however, while achieving limited non-abrasive qualities impart other undesirable properties to the fiberboard. By way of illustration, glycerin has been used in the past to impart a non-abrasive surface to fiberboard. However, a glycerin coat decreases the strength of the board, increases its water absorbency and imparts an objectionable damp feel to the board. Likewise, prior non-abrasive coating compounds, such as sodium oleate, exhibit poor aging qualities with the inherent resultant being that the coated board often develops an objectionable odor. Or, with wax coating, the coating tends to wear away easily and detrimentally affect the surface. Other prior art coatings have been difiicult and expensive to apply and often ineffective for the intended purpose. Thus, the disadvantages of their use far outweigh the advantages.

nited States Patent O "ice It will be appreciated by those skilled in the art that if paper or paperboard is coated by a method with compositions producing excellent scuff-resistance, the tendency to avoid peeling and quills would satisfactorily increase the usefulness of the paper or board. Likewise, 1t will be appreciated by those skilled in the art that if paper or paperboard is coated with a composition having excellent non-abrasive properties which decreases the possibility of scuifs, scratches, wear spots, flaws, etc. on articles of commerce, such compositions and methods would have a positive use and a definite commercial value.

It will be further appreciated by those skilled in the art that paper and paperboard coated with a scuff-resistant non-abrasive coating which does not decrease the tensile strength of the paper or board, or increase the water'absorbency characteristics or impart an objectionable odor will represent a useful contribution to the art.

Accordingly, it is an object of this invention to provide a method for increasing the scuff-resistance of paper and paperboard.

Another object of this invention is to provide a method for applying scuff-resistant coatings to paper and paperboard.

Still another object of this invention is to provide a scuff-resistant composition for coating paper and paperboard.

Yet another object of this invention is to provide a scratch-resistant surface that is inexpensive and easy to apply and overcomes the difficulties and tribulations associated with the prior art.

A still further object of this invention is to provide scuff-resistant non-abrasive surfaces to paper and paper type products.

Other objects, features and advantages of this invention will become evident from the following detailed description of the manner and mode of practicing the invention.

In attaining the objects of this invention, it has now been surprisingly found that a scuff-resistant surface can be imparted to paper and paperboard by treating said paper or board with a tin compound which tin treated paper or board is then coated with an aqueous emulsion of polyethylene.

In carrying out the instant invention, the paper or board is first treated with a tin compound. The tin compound may be applied to the surface to be treated by various means conventional in the art, dipping, spraying, knife coating, roll coating, air coating, extrude coating, etc. The tin compound employed in this invention may be in the oxidized or reduced state. That is, the tin compound is multivalent, the multivalent metal can change its valence state reversibly. -As examples of tin compounds may be cited stannic halides, for example, stannic bromide, stannic chloride, etc., stannic ammonium chloride, stannic oxide, stannic oxychloride, stannous chloride, stannous oxide, stannous dichloride, stannous oleate, stannous stea-rate and the like.

The tin compound is preferably applied to the surface in a dilute solution, that is, the tin compound is dissolved in a solvent. The diluents that can be used in the process are those which are generally soluble for the respective tin compounds and include alcohols, aliphatic hydrocarbons, cycloaliphatic hydrocarbons, aromatic hydrocarbons and halogenated hydrocarbons. Examples of suitable diluents that can be employed include ethyl alcohol, isopropyl alcohol, benzene, toluene, n-heptane, cyclohexane and the like.

The amount of tin effective for the purpose of the invention may vary depending on the kind of paper being treated, the method of application used and the nature of the tin compound. Generally, the concentration range of the tin compound will range from about 1 to about 10 percent, with the now preferred range being about 3 percent to about 6 percent. Lesser amounts or greater amounts are effective to produce some coating, and the desired concentration may be easily ascertained by those knowledged in the art. By way of illustration, a primary coating composition is prepared by dissolving 4.5 grams of stannous chloride in 95.5 grams of isopropyl alcohol, to give a 4.5 percent solution.

The second coating composition which is employed in the present invention is an organic coating containing polyethylene. The polyethylene emulsion now preferred is an aqueous emulsion containing AC Polyethylene, Product No. 629, distributed by the Semet-Solvay Division of Allied Chemical and Dye Corporation. By way of illustration, an emulsion is prepared by melting 40 parts of partially-oxidized, low molecular weight polyethylene having a molecular weight of approximately 1200-2000 and an acid number of 14 to 17, and adding thereto 11 parts of a fatty acid such as oleic, palmitic, stearic, lauric or mixtures thereof. Two parts of an aqueous solution of an alkali metal hydroxide are then added to the mixture while the mixture is at a temperature of from 230-245 F. Water is also added in an amount of 207 parts. The polyethylene has a particle size of less than 10 microns, usually from 1 to microns, and comprises a solid content of about 20 percent by weight of the emulsion. A now preferred composition has the following proportions in approximate parts by weight:

Parts Polyethylene, A.C. No. 629 40 Oleic acid 11 Potassium hydroxide 2 Distilled water 207 The above emulsion, containing 20 percentby weight solid, was diluted with water 75 percent to 25 percent, that is water to emulsion on a volume basis.

The following examples are merely illustrative of the present invention and should not be considered limiting its scope in any way.

EXAMPLE I Commercially available kraft paper was treated by dipping it into a 4.5 percent solution of stannous chloride for 2 minutes, then air dried for 15 minutes. The tin t-reated paper was then heated in an oven at 135 C. for 2 hours.

EXAMPLE If Kraft paper was treated by spraying the paper on the wire side with an aqueous emulsion of the polyethylene coating prepared above. The emulsion was sprayed onto warm paper.

EXAMPLE III A kraft paper treated by dipping into a 4.5 percent solution of stannous chloride was air dried for 15 minutes. Next, the tin treated paper was placed into an oven for 2 hours at 135 C. The sheet was then sprayed on the wire side and while still warm, with the aqueous emulsion prepared above.

Paper strips treated in accordance with the foregoing examples were tested for scuif resistance to evaluate the effectiveness of the respective coatings. The test for scuff resistance of paper or paperboard that has been set up is to measure the ability of a given piece of paper or board to resist scufling and is conducted by rubbing corresponding flat surfaces of two specimens against each other. The test is designed to determine whether paper or board might fail or perform satisfactorily under such conditions.

The test is conducted by rubbing corresponding flat surfaces of two specimens against each other. One specimen is attached tautly to a fixed smooth flat plate, the other specimen is clamped to a movable plate and is rubbed against the other. The movable plate is driven by an eccentric arm and carries a dead weight load of 30 lbs. The eccentric drive wheel revolves at 96 rpm. with a stroke of approximately 4 inches. The number of strokes as counted by the machine represents both the forward and the backward movement over the paper, that is, a stroke is a cycle of two movements. Untreated paper, paper treated with tin alone, paper treated with polyethylene emulsion and paper treated with both tin and the emulsion were rubbed on the wire side for scuffresistance. The test was terminated when the value of 350 was reached. At this value, there was no evidence of scufling. This value is greater than the scuffing which a paper product would be subjected to in actual commerce. The results tabulated below are results of the scuff test:

The above tests clearly establish the unobvious soulfresistance that is obtained by the present invention. The untreated paper after a few strokes showed very distinct scuifs and peeling. The paper treated with the tin alone showed the destructive signs of scutis and peeling with but a few more strokes than the untreated paper. The results for the emulsion alone were also of a very low order of resistance. By way of contrast, the paper treated with the dual coating exhibited a pronounced high order of resistance. It is evident that the dual coating of tin and the emulsion produues a superior scuff resistant product when compared with tin alone or polyethylene emulsion alone. Also, the tests further demonstrate that the results obtained are greater than the sum of the separate coatings, clearly indicating an unobvious, unexpected synergistic result.

While the illustrative embodiments of the invention have been described with particularity, it will be understood that various modifications will be apparent and can readily be made by those skilled in the art without departing from the scope and spirit of the invention.

I claim:

1. A process for treating paperboard, to increase its send-resistance Which comprises applying to said paperboard an effective amount of a solution of tin compound, wherein said tin compound is a member selected from the group consisting of stannic bromide, stannic chloride, stannic ammonium chloride, stannic oxide, stannic oxychloride, stannous chloride, stannous oxide, stannous dichloride, stannous oleate and stannous stearate, drying the paperboard at an elevated temperature, and applying to said paperboard an effective amount of an aqueous emulsion of polyethylene while said paperboard is still at said elevated temperature.

References Cited UNITED STATES PATENTS 2,943,955 7/1960 Brill 117-152 X 3,230,135 1/1966 Hurst.

3,255,035 6/1966 Clough et a1 117-l52 X 3,323,889 6/ 1967 Carl et al. 1l7-72 X WILLIAM D. MARTIN, Primary Examiner R. HUSACK, Assistant Examiner US. or. X.R. 117-1s2, 

